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FSD1000 Datasheet(PDF) 3 Page - Fairchild Semiconductor |
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FSD1000 Datasheet(HTML) 3 Page - Fairchild Semiconductor |
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FSD1000 3 Pin Definitions Pin Number Pin Name Pin Function Description 1VFB,AUX This pin is for the feedback control of the auxiliary power. This pin is internally connected to the inverting input of the PWM comparator. The collector of an opto-coupler is typically tied to this pin. For stable operation, a capacitor should be placed between this pin and GND. Voltage mode control is employed for the auxiliary power and the duty cycle ratio of Internal MOSFET for the auxiliary power is proportional to the voltage of this pin. If the voltage of this pin exceeds 4.5V, the over load protection is triggered terminating the switching operation of the main and auxiliary power (Auto-restart mode protection). 2VFB,MAIN This pin is for the feedback control of the main power. This pin is internally connected to the inverting input of the PWM comparator. The collector of an opto-coupler is typically tied to this pin. For stable operation, a capacitor should be placed between this pin and GND. Current mode control is employed for the main power and the peak drain current of the external MOSFET for the main power is proportional to the voltage of this pin. If the voltage of this pin exceeds 7V, the over load protection is triggered disabling the gating output for the main power (Latch mode protection). 3S/S This pin is for the soft start of the main power. Soft start time is programmed by a capacitor on this pin. 4 Output This pin is for the gate drive of the external MOSFET of the main power. 5Vcc This pin is the positive supply voltage input. During startup, the power is supplied by an internal high voltage current source that is connected to the Vstr pin. When Vcc reaches 13.5V, the internal high voltage current source is disabled and the power is supplied from auxiliary transformer winding. 6ISENSE This pin is for the current sense of the external MOSFET for the main power. It is internally connected to the PWM comparator for the main. 7LS1 This pin is for line under voltage detection. When the voltage of this in drops below 1.4V the main power is shutdown. When the voltage drops below 0.8V, the auxiliary power is shutdown. 8LS2 This pin is for line over voltage detection and maximum duty cycle ratio change. The maximum duty cycle ratio is set to be 50% when the voltage of LS2 pin is higher than 2.4V. The maximum duty cycle ratio is increased to 67% when LS2 voltage goes below 2.0V. When the voltage of LS2 goes above 4.4V, the switching operations for the main and auxiliary powers are disabled to protect the switching devices. 9ILIM This pin is for the current limit of the auxiliary power. The pulse-by-pulse current limit level of the internal SenseFET is programmed by a resistor on this pin. 10 NC 11 Drain This pin is the high voltage power SenseFET drain. It is designed to drive the auxiliary transformer directly. 12 VSTR This pin is connected directly to the high voltage DC link. At startup, the internal high voltage current source supplies internal bias and charges the external capacitor that is connected to the Vcc pin. Once Vcc reaches 13V, the internal current source is disabled. |
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